Adhesive composition comprising crosslinked maleic ester copolymers, method of preparation and a backing coated with said composition



States John (3. Sellers, Nixon, N. J., assignor to Johnson & .lohrn son, a corporation of New Jersey N Drawing. Application September 16, 1953 Serial No. 380,595

4 Claims. (Cl. 260-785) This invention relates to adhesives and, in preferred embodiments, to compositions which may be used as pressure-sensitive adhesives. More particularly, it relates to esterified copolymers of maleic anhydride and a vinyl ether which are cross-linked by heating in the presence of added peroxide polymerization catalyst. Corresponding copolymer esters which are cross-linked by reaction with a polyvalent metal oxide or with a polyhydric alcohol are claimed in divisional applications, Serial Numbers 758,888 and 758,889, filed September 4, 1958.

In manufacture of known adhesives it has been necessary to compound several ingredients in order to arrive at an acceptable formulation. In manufacture of tape, notably transparent pressure-sensitive tapes, or tapes used for surgical purposes, it has been the usual practice to compound together, for example on a heated mill equal parts of an elastomer, a tackifier and a pigment or filler. It has further been found necessary to add a substantial amount of plasticizer in order to provide the desired plastic properties and to permit the adhesive to be readily applied to the backing. An additional ingredient, nearly always found necessary, is a stabilizer, e. g. an antioxidant, which tends to impart resistance to aging condi tions such as air, heat and sunlight. The compounding of these various ingredients itself has constituted a significant problem since it has been necessary to mix them on a pair of rolls which is a time-consuming and expensive operation. With so many ingredients, variations 'in supply and quality of raw materials have been found to give rise to serious difiiculty. The elastomer and the tackifier are particularly susceptible to these circumstances. Even after obtaining the compounded adhesive, ones difiiculties were not always finally resolved. it has frequently been impractical to obtain the degree of tack and tensile strength in the end product adhesive since these variables are ditficult to control and frequently could not be controlled to the extent nor within the range desired. Migration of the plasticizer from the adhesive composition into surrounding areas or to adiacent films or layers has also been the cause of considerable difliculty.

Objects and advantages of the present invention are solution of problems which arise by reason of the abovelisted disadvantages in prior art adhesives. One object is to produce an adhesive having high stick properties which does not require the presence of a tackifier and, in particular, an adhesive which may be compounded to'stick to an unprimed cellulosic film such as ethyl cellulose 01' cellulose acetate. A further advantage of the invention is that compounds have been discovered which may be so constituted that they will have plasticity and other properties variable over a wide range, but reproducible and controllable by the method of preparation. Another object of the invention is to provide compounds which have high tensile strength and approach water whiteness so that they may be used in pressure-sensitive commercial transparent tapes.

Still another object of the invention is to provide, ac-

cording to one form of the invention, and adhesive com pound which may be used, preferably without plasticizer, and will be stable, that is, resistant to aging conditions such as heat, sunlight and air without the need for a stabilizer.

The adhesive compounds of the present invention are certain esters of maleic anhydride-vinyl ether copolymers. Compounds possessing peculiarly valuable adhesive properties according to the, invention are such copolymers esterified to the extent of at least 65% of the total potential carboxyl content with a primary aliphatic alcohol having 6 to 16 carbon atoms, inclusive. The invention is also directed to the method of preparing these compounds and their use in certain articles .such as tapes, surgical dressings, and other articles having a supporting surface with a layer of the invention adhesive coated thereon.

An important advantage of the invention is the provision of adhesives which may be cured to an insoluble, solvent-resistant, heat-resistant material, and still remain pressure-sensitive. In marked contrast to prior art adhesives, which generally will stick to themselves tenaciously but to other objects with relatively little force, the invention adhesive is characterized by tenacious adhesion to other objects such as the human skin, but relatively little adhesion to itself. Hence, adhesive tape made from invention adhesive will not stick to itself to the degree that separation is prevented without disruption of the mass of undue deformation of the tape backing.

The vinyl ether-maleic anhydride polymers of the invention are prepared by catalytic copolymerization of the monomers in a solvent, preferably a nonaqueous solvent such as xylene or benzene, and in an inert atmosphere such as nitrogen. Approximately equimolecular amounts of the monomers are first dissolved in the solvent. The solution is then heated to reaction temperature which is in the range above about 40 C. to the boiling point of the solution, and maintained at this level until the reaction has progressed to completion. At higher temperatures, of course, the reaction proceeds at a faster rate. It has been found that the reaction rate may be best controlled at temperatures in the range 40 to C., and hence this temperature range is preferred. If desired, the reaction rate may be effectively controlled at higher temperature levels by adding the vinyl ether and catalyst stepwise.

The molecular weight of the maleic anhydride-vinyl ether polymer is controlled by controlling primarily three variables, 'i. e. the temperature, the catalyst concentration and the solvent utilized for carrying out the polymerization. Higher temperatures tend to produce low molecular weight polymers and, conversely, low temperatures tend to produce higher molecular weight copolymers. A peroxide catalyst, such as benzoyl peroxide, which is soluble in the solvent medium is added to catalyze the reaction, which is a chain type reaction. There is a tendency on the part of the solvent to interfere to a degree with the polymerization, that is, to combine with the free radical which promotes the reaction, and thereby terminate the reaction at the point at which the polymerization has progressed on a particular chain. This interference on the part of the solvent has been designatedby an index known as the transfer constant, a term proposed and defined by Mayo, Journal. of the American Chemical Society, vol. 65, 1943, pages 2324 to 2329. Solvents having a low transfer constant exhibit relatively slight tendency to interfere with chainereaction typev polymerization- Benzene is' an example of this type solvent. On the other hand, solvents having a relatively high constant tendto have high degree of interference with the polymerization. Xyleneis an example of the latter type solvent. When a solvent having a lower transfer constant is used the molecular weight of the polymer Patented Dec. 30, 1958 is sensitive to the concentration of catalyst,- iarger amounts of catalyst tending to produce lower molecular weight polymers. The low constant solvents tend to produce higher moleeular weight polymers, and thehi-gher constant solvents tend to produce lower molecular weight polymers. However, theu'se of a higher constant solvent such as xylene is not precluded where high molecular weight polymers are desired since the tendency of the xylene to lower the molecular weight may be counteracted to some extent t by operating. at a lower reaction temperature.

As anexampleof-copolymeriaation oflmaleic anhydride. and vinyl ether,"1.- mol 'of maleic anhydride is dissolved.

in 600 parts' of Xylene as} solvent." The reaction vessel is provided with a superjacent vented reflux condenser; Heat is applied tome vessel while stirring its contents and whilegaseous N -is beingpassed through the vessel untilaternperature 0&65' C.'-is attaincd. At this point 1.0 'mol" of ethyl vinyl ether and 0.33 parts of benzoyl peroxide catalyst are added and the'=65' C. t temperature r.

and stirring continued until reaction is complete. The polymer precipitates as it is formed. it Themixture of polymer and solvent produced may be used for prep-, aration ofp'olymerester such as:by adding appropriate amounts of alcohol, antioxidant and esterification catalyst as indicated below, or the polymer and solvent may beseparated by'filtration prior to esterifying the polymer. Any possible small amounts of unrea'cted monomers-will be removed from thesystem during purification following esterification.

Attempts to polymerize'rnaleic ester with vinyl other have suffered from the tendency ot the ester and ether to polymerize in-ratios other thanth'at sought for according to the presentinvention. Further, it is difiicult to obtain the high molecular weightsand plasticities-which are important properties of the invention products. Hence, the'invention prodiictsare preterablymade by using the maleic anhydride as monomer, rather than an ester thereofl.

The index. of polymer molecular wcigh'tisthe intrinsic viscosity of the polymer. is measuredby preparing a dilute solutiongofithe polymer in cyclohexanon'e assolvent, andcarrying out intrinsic viscosity measurement at 30 C. according to knowmprocedure. For example, a cyclohexanone solution of 1 thepolymer having 1 gram 'of polymer per 100cc; of-solution is prepared, and several dilutions of this solution, e. g; to 0.7 grams per 100 cc. and 0.5 gramper 100 cc., are made; Flow times arethen mcasuredat 30 G1 on a'general purpose Qstwald' viscosimetefpipette having a capillary about 0.5 mm; in diameter andadengthof'about15*cm; The relative viscosity at each, concentrationis calculated. Relativ'e'viscosity is the ratio or the'fliiw time of the resin solution tothe flow time of the solvent. Specific viscosity. is defined as the'relative viscosity minus one. Re-

duced specific viscosity is defined as are specific viscosity divided by the" concentration irr'grams perlOO ml. of solution; ,A plot 'ismade of reducedspecific viscosity vs. concentration and the straigh tline soobtained is extrapolated tozero concentration. Thevalue of the reduced specific viscosity at zeroconcentration is known as the intrinsic viscosity.

polymermolecular-wei'ght as measured by intrinsic viscosity eirerts a notableand iniportantetiect upon the properties of the final ester adhesive as will appear more clearly below. molecular-weightlpolymers tend to produce adhesivesmaving higher plasticity, and low''mo'- lecular weight polymers tend to produce adhesives .baving low plasticity, Suitable polymers are those having viscosities withinthe approximate range 0'2""to 2.0 whilepreferred polymersihjave viseosities the approximate range 0.41:, 1.1., The factorof plasticity andits efl eet upon properties of. the adhesiveis-gone into more fully below whereupdnthe importance of controlling'the poly.- mer viscosity will be appreciated.

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The vinyl.ether.used. as. monomer for preparation of the invention polymers may be any of the low molecular weight vinyl ethers, that is, those having one to eight carbon atoms, inclusive, in the aliphatic group. Methyl, ethyl, propyl, isopropyl, butyl and isobutyl vinyl ethers are readily polymerizable and hence notably satisfactory. The general formula of the ethers is:

where R is alkyl having 1-8 carbon atoms, preferably. 1-2 carbon atoms, inclusive, and X is a. substituent such as low molecular weight alkyl,.that does not seriously interfere with the stability, nor the polymerizability of the vinyl ether. As the ether molecular weight increases, some plasticizing' effect upon thefinalipolymer is introduced, but the higher molecular weight ethers may be found somewhat.more difiicult to co-polymerize with the maleic anhydride;

Both thevinyl' ether and the maleic anhydride polymerize with the-other monomer rather than withitself, andhence theratioiofmonomersxin the copolymer is one to one.

The particular'alcohol used to esterify the polymer ester has animportant effect upon the. properties, such as plasticity, of the final adhesive produced. The ten carbon atom alcohols produce adhesives having, lowest plasticity, i. e. the softest adhesives. As alcohol molecular weight is decreased below n-decyl alcohol the tendency istoproduce adhesives which are harder, i. e. have a higher plasticity. As alcohol molecular weight is increased above 10, thepolymer esters again increase in plasticity. The choice of alcohol is a convenient variable which may be employed in producing an adhesive h'avingtthe particular sought-for properties in any case. Generally, satisfactory adhesives may be. prepared from primary monohydric aliphatic alcohols having- 6 to 16 carbon atoms, inclusive. These may beeither straight or branch chain alcohols. The straight chain alcohols are, however, preferred since they tend to produce. softer and tackier adhesives, therebygiving more latitude in manufacture of an adhesive having specificsought-for properties. The lower carbon atom alcohols and the high carbon atom alcohols within the-broad range may find particular utility as laminating, adhesives since. they tendto be harder. However, as'indicated above, it is an important. advantage of the invention to manufacture pressure-sensitive adhesives which donot-require use of. plasticizersor tackifiers. Alcohols having. 6m 16 carbon atoms, inclusive, are thereforepreferred.for manufactureof pressure-sensitive adhesives. since the. degree of softness and plasticity of. adhesives obtained by use of. alcohols withinthis range is such that tackifiers and plasticizers may be. dispensed with. Normal decyl a1- cohol, n-octyl, n hexyland lauryl alcohols are preferred materials for manufacture of adhesives according to the invention. Another very suitable alcohol is known as CPS 224, a product of Erijay, Standard Oil Company of New Jersey, which is a mixture of alcohols containing a high proportion of branch. chain decyl. alcohols. Other satisfactory alcohols for manufacture of pressure-semi tive adhesives are n-nonyl, iso-octyl (Enjay), tridecyl (Enjay) and 'n-undecyl alcohols.

The percentage of esterification of the copolymers is another factor having an important effect upon the adhesives. Percent. esterification is defined as the overall percentage of. total potential .carboxyl. groups on the polymer. chains: that are intheform offth'e ester group COOR,. where R is the. alkyl part of the alcohol. Potential carboxyl' groups include carboxyl groups as such and groups capable. of yielding the carboxylgroup by hydrolysis and having the formula where X is hydrogen, alkyl, metal or carbon'(e. g. as in the case of the anhydride). The higher the percentage of esterification, the greater the tack possessed by the adhesives and the softer the adhesive becomes. Below 65% esterification, the esters possess insuflicient tack for invention purposes. The important sought-for properties of the invention adhesives begin to become apparent at percent of esterification above 65 Hence, the invention contemplates adhesives esterified in the range of 65 to 100%. Adhesives in the lower portion of this range possess inherent tacky properties but may be harder so as to require the addition of certain amounts of plasticizers. However, at percent of esterification above about 80-85%, suflicient alcohol will have been incorporated into the adhesive to impart softness so that addition of extraneous plasticizer is not necessary, and the adhesives will be found to be self-plasticized.

The percent of esterification is also important from the standpoint of leaving enough unreacted carboxyl groups to permit cross-linking of the polymer chain by reinforcing action between unesterified carboxyls, as will be more fully explained below. Below about 95% esterification it will generally be found that there are suflicient unreacted, i. e. unesterified, carboxyl groups to permit desired cross-linking of polymer chains by reinforcing action. Hence, in one embodiment of the invention a range of esterification of particular importance is approximately 80-85 to 95%. As previously indicated, higher percentage of esterification tends to produce adhesives which are softer. However, even at esterifications approaching 100% the plasticity of the adhesive can be controlled by choice of molecular weight alcohol and degree of polymerization of maleic anhydride-vinyl ether copolymer. Further, the higher the esterification of the copolymer, the less is its tendency to cross-link during heating, aging, etc., and hence the greater its stability. Adhesives approaching esterification of 100% have the outstanding advantage of optimum degree of tack. Their softness and tendency to cold flow can be controlled by methods explained below.

Reaction conditions for esterification of the polymer are important in obtaining the high percentages of esterification required according to the present invention.

The esterification reaction of the copolymer is preferably, though not necessarily, carried out in the same solvent that was used for polymerization. However, the polymer raw material may be purchased, and dissolved in solvent rather than synthesized. A molar excess of the desired alcohol is added to the solution together with an anti-oxidant and catalyst. Suitable anti-oxidants include 2 ,5-ditertiarybutylhydroquinone, 2,6-ditertiary butyl p-cresol, and others known in the art, while as catalysts p-toluene sulfonic acid, benzene sulfonic acid, sulfuric acid and many others are satisfactory. The solution is then boiled and water of esterification removed until reaction is substantially complete. The completeness of the reaction is observed by the rate of removal of water and when the rate becomes insignificant the reaction is considered as being substantially complete. Hydrocarbons, preferably aromatic hydrocarbons, boiling above 100 C. are suitable solvents. Using diethyl benzene as a solvent (boiling point 182 C.) completion of the :reaction may occur in about 70 minutes. With xylene (B. P. 139144 C.) the reaction may take 7 to 8 hours, 'while with toluene (B. P. 110.6 C.) 12 or more hours may be required for substantially complete esterification. The concentration of esterification catalyst has considerable effect upon the rate of reaction; After the esterification reaction has progressed to the desired degree the reaction is terminated by cooling the reaction mass.

Various procedures may be used for recovering the adhesive from the solution. For example, the reaction mass after esterification may be placed in a vessel fitted with a mechanical agitator and an outlet at the bottom. Methanol may then be added, with stirring, until the ester just precipitates sufficiently to form two distinct layers upon being allowed to settle. The ester is drawn off from the bottom of the flask. The methanol layer, containing impurities, may be treated to recover solvents, as by distillation. The ester is put back into the vessel and just enough toluene or benzene added to redissolve it. Again, methanol is added until the ester just precipitates. It is allowed to settle, and again separated from the methanol layer. This procedure is repeated twice more. At this point the ester will have acquired a very light yellow color. Generally, a total amount of methanol equal to only one-half the volume of original ester solution is required for purification.

An alternative procedure for recovering adhesive which is -95% or more esterified is to pour the reaction mass after cooling into a sufficient amount of acetone to cause recipitation of the polymer. The liquid is decanted and the polymer is washed with small amounts of acetone. The polymer at this stage will be almost water-white.

The polymer solution after purification may be treated with a small amount, i. e. 2%, of an anti-oxidant stabilizer such as 2,5-ditertiarybutylhydroquinone to stabilize the polymer during drying. The solution is then evapo-' rated on a steam bath and the semi-dried polymer is dried in a vacuum chamber at C. and 15 inches of mercury absolute pressure.

Polymer ester plasticity is a key property determining its suitability for use in various types of adhesives. The plasticity should 'be high enough to afford adequately high tensile strength and low enough so that it can be successfully worked and calendered'or spread onto the sheet. Plasticity is measured on a cylindrical pellet of adhesive mass 16 mm. in diameter and weighing 2.00 grams by placing the pellet on a parallel plate plastometer, otherwise known as a Williams plastometer, of the type manufactured, for example, by the Scott in strument Company, and maintaining the pellet and surroundings at 100 F. and under a 5000 gram load, and noting the height of the pellet after 14 minutes. This height in millimeters is taken as a measurement of plasticity. For invention purposes, polymer esters having plasticity so low as to be outside the range of accurate measurement on the instrument may be satisfactory. Methods are available to increase plasticity, as will be explained below. The desired plasticity is obtained, as implied above, by controlling viscosity of the copolymer (high viscosities tend to produce high plasticities), controlling the alcohol used for esterification (alcohols having very high or very low molecular weight tend to produce adhesives having high plasticities), and controlling the degree ofesterification (high esterification tends to produce low plasticity). On the other hand, adhesives which have higher plasticities, that is, above the range of those which may be used unplasticized as pressure-sensitive adhesives may be used as laminating adhesives or, by incorporating suitable amounts of plasticizer, as pressuresensitive adhesives. However, adhesives in the plasticity range substantially above 4.0 mm. are less advantageous when plasticized for use as pressure-sensitive adhesives since they may lack the necessary cohesive strength. It is generally endeavored to produce adhesives having plasticities not substantially above 4.0 mm. The preferred range of plasticity is in the approximate region 0.7-3.0 mm., since within this range polymer esters have plasticity such that no plasticizer is necessary to produce adhesive masses having a high degree of tack and pressure-sensitivity.

As indicated above, there is a tendency on the part of certain of the invention adhesives to exhibit some cold flow, that is, lack of body, and susceptibility to plastic flow over long periods of time when under stress. This phenomenon may be overcome by cross-linking the polymer ester chains. Cross-linking may be obtained by formation of reinforcing bonds between unreacted car boxyl groups on adjacent polymer chains. This type of 7 cross-linking may" be produced by a polyvalent metal oxide typ filler (including hyd'rates} such as zinc oxide, titanium dioxide or aluminum hydrate; The metallic oxide compound in any case may' be dispersed in the adhesives in a ball mill or paint mill, or canbe mixed on the rolls. The controlling factor information of reinforcing bonds is thepercentage free, i. e. unestertfied, carboxyl groups in the polymer ester rather than the amount of metal oxides present since very small amounts of metal oxide will accomplish ahigh degree of cross-linking. In the case where cross-linking and gelling of the adhesive ester is relied upon to impart resistance to cold flow, the percent of esterification as indicated above, is of importance. Therange 80-"-85 to 95% esterification defines the' content of free carboxyls which will afford adequate cross-linking. Above about 95% esterification the polymer esters arerelativcly immune to cross-linking by fbrmation' of reinforcing bonds.

Another convenient way of imparting resistance to cold How to a polymer ester is'to incorporate auadequate amount of a copolymer ester adhesive which has previously been cross linked, either by the reinforcing bond formation as previously described" or byperoxide reaction, described below, since'such gelled materials are quite compatible-withthe adhesive.

The alternative and preferred manner of effecting polymer cross-linking is to carry out a chain type reaction by addition of a free radical type polymerization catalyst, e. g. a peroxide-catalyst suchuas benzoyl peroxide. This is accomplishedby adding to the purified solution of adhesive ester in a solvent such as toluene, an amount of the benzoyl peroxide ores-linking catalyst in the range 0.1 to based'ou the ester, heating the solution-to remove solvent atabout 100 C., heating-the residue for time to accomplish cross-linking which will generally be in the range 5 to 60 minutes, and then terminating the cross-linkingreaction by heating until all peroxide has been decomposed, e. g., overnight, at 100 C. in the case of benzoyl'peroxide.

An index of the degree of cross-linking is gel content, which may be determined as follows, 0.4 gm. of adhesive is mixed withl00 cc. of benzene and allowed to stand'without stirring for48 hours at 30 C. The mixture is then poured throughastandard stainless steel wire screen of 100 mesh. cc. ofthe filtrate are evaporated to dryness at 100 C. andthe residue-weighed. The gel content is taken at 100 minus the percentage of the original sample of adhesive'whichdissolved. High gel content, ofcourse, reflects high degree of cross-linkage. Further, the degree of cross-linking required in order to reduce coldfi ow to the sought-for levels specified below will be determinedto, a large extent by the plasticity of'theester, lowplasticity polymer esters requiring gencrally more'cross-li'nkin'gthan high plasticityesters. From the standpoint'of sufficient cross-linking to reduce cold flow to acceptablejlevels, even for the higher plasticity esters, minimum gel'content'of about 10% is desirable for"materialjcross-linked either in the first instance orby addition of. previously cross-linked ester. Where consistent withmaximum plasticity limitations, gel content of invention products may be as high as 100%.

lithe occasion requires, cross=linkingfmay beefiected by botlfmetaloxide and peroxideiaction. In place of a peroxide any of the cross-'linking'agents employed as rubber-curing agents, i. e. those which operateby afree radical mechanism, may be utilized.

The property of cold flow maybe measured by sticking aball amneadhesive weighing 310 gms. against a vertical glass plate and noting the downward flow in inches due to gravity for'a period'of'24'hours at room temperature. Particularly suitable" pressure-sensitive" adhesives; of the invention areithosvwhichare cross-linked to the' extent that cold fiowQis not greater than 2 inchesastmeasured bythis-standardmethod.

Among theoutstandingadvantnges of the invention 8. products is their ability to stick to unprimed'film, e. g. cellulosie films such as ethyl cellulose,,cellulose acetate, or'(when cross-linked) to-regenerated cellulose. T head hesivecompounds further have the property of sticking to unprimed films of polyvinyl chloride resin, and polyethylene glycol-terephthalic acid film which is marketed by E. I. du Pont de Nemours & Company under the trademark Mylar.

The advantages of the invention composition are especially outstanding in respect to adhesiveness;.particularly pressure sensitivity. However, the novel-compositions of the invention possess other advantageous properties which render them suitable for other applications. For example, by cross-linking the products, one may obtain a bonding material which is insoluble in solvents and resistant toelcvated' temperature, and hence is suitable for manufacture ofplywood or glass fiber laminates. Certainof the invention products may be incorporated in coatings as curing resins.- They possess unusually strong adhesion to glass and metal, good gloss, and can be cured by baking with a free radical type catalyst. At temperatures below that of. pressure sensitivity the invention products are also-applicable to injection molding where curing is desired.

The following examples are presented as illustrating rather than limiting. the scope of theinvention. Parts and percentages are on a weight basis unless'otherwise specified.

Example I An esterification vessel was fitted with an azeotropic trap and stirrer and the followingmaterials were placed therein: 39 parts vinyl methyl ether-maleic anhydride copolymer having intrinsic viscosity 1.66, 102 parts lauryl alcohol, 5 parts p-toluene sulfonic acid, 8 parts 2,5-cli tertiarybutylhydroquinone' and 344' parts xylene. The mixture'was heated to boiling whereupon the copolymer and other ingredients wentinto solution. Refluxingwas continued'for 3 hours'during which time 4.5 parts of water were collected in the azeotropic trap. The esterification reaction was substantially complete as evidenced by decreasein rateof removal of water of esterification. The solution was cooled and poured into just sufiicient methanol to cause precipitation. After phase separation, the precipitate was treatedwitb' just enough benzene to dissolve it. The polymer ester was again'precipitated and dissolved'as above, and reprecipitated and washed several times with'small amounts ofmethanol. The wet precipitate was dried on a steam bath and finally more thoroughly driedlat C. and 15in. mercury absolutepressure. The" product was extremely tacky, almost Waterwhite and had plasticity of 1.30 'mm. Percent estcrification was about 94%. Adhesive masses foruse as surgical adhesives may be made by milling the polymer ester with 40-50% of zinc oxide, titanium dioxideor aluminum hydrate, etc. Alternatively, the masses maybe crosslinked according to the peroxide procedure described above and exemplified in Example XI. These masses are spread on primed vinyl film, cloth or waterproof cloth.

Example -II which time 9.8parts water'werecollectedinthe azeotropic trap. The pol-ymerester was recoveredan'dpuriliedaccording to the procedure described in Exainplcl. It was extremely tacky, almost-water-whitc and--had plasticity of 073mm. Percent esterification-w'as86%.-

Example III 39*parts ofvinyl methyl ether-maleic anhydride copolymer having intrinsic viscosity of 0.73" were placed Example IV In the esterification apparatus described in Example I there were placed 156 parts vinyl methyl ether-maleic anhydride copolymer, intrinsic viscosity 0.73, 312 parts n-octyl alcohol, 14.5 parts p-toluene sulfonic acid, 22.5 p'arts 2,5-ditertiarybutylhydroquinone and 515 parts Xylene. The mixture was refluxed for /2 hours, and 22 parts water were collected. Plasticity of the purified and dried product, which was extremely tacky, was 0.98. Percent esterification was 94%.

Example V Into the esterification apparatus of Example I there were placed 39 parts of vinyl methyl ether-maleic anhydride 'copolymer having intrinsic viscosity 0.73, 95 parts n-decyl alcohol, 4 parts p-toluene sulfonic acid, 7 parts 2,5-'ditertiarybutylhydroquinone and 172 parts xylene. The mixture was refluxed for 5 hours, and 6.2 parts water were collected in the azeotropic trap. The polymer ester, after purifying and drying, was found to be extremely tacky and have plasticity less than 0.65. The percent esterification was 94%.

Example VI In the esterification apparatus described in Example I therewere placed 39 parts vinyl methyl ether-maleic anhydride copolymer having intrinsic viscosity 0.73, 95 parts of a mixture of alcohols containing a high proportion of branch chain decyl alcohols known in the trade as fCPS 224, a product of Enjay, Standard Oil Company of New Jersey, 4 parts p-toluene sulfonic acid, 7 parts '2,S-ditertiarybutylhydroquinone and 172 parts xylene. The mixture was refluxed for 9% hours, and 7.1 parts water were collected. The polymer ester, after separation, purification and drying, was found to be extremely tacky and have plasticity less than 0.65. Percent esterification was 99%.

Example VII --39'parts vinyl methyl ether-maleic anhydride copolymer having intrinsic viscosity 0.73, 78 parts iso-octyl alcbhbl, 3.5 parts p-toluene sulfonic acid, 6.5 parts 2,5- ditertiarybutylhydroquinone, and 172 parts xylene were placed in an esterification apparatus and refluxed for 9 hours. 8.3 parts water were collected in the azeotropic trap. The polymer ester, after recovery, purification and drying, was extremely tacky, and had plasticity of 1.14. Yield was 87% of theory. Percent esterification was i Example VIII In an esterification apparatus fitted with an azeotropic trap and a mechanical stirrer were placed 156 parts maleic anhydride-vinyl methyl ether copolymer, intrinsic visc'osity 0.73, 312 parts n-octanol, 14.5 parts p-toluene sulfonic acid, 22.5 parts 2,5-ditertiarybutylhydroquinone, and 5 parts xylene. The mixture was heated to boiling, refluxedyand water was removed in the azeotropic trap. 7- samples were removed from the esterification vessel at various times during the reaction. Pere'cent esterification was calculated for each sample from the amount of water collected at the time of removal. The first two samples were precipitated and purified with petroleum ether and the remainingsamples were preci'pitated' and purified with methanol. Several redissolv a a n;

"in. ings and reprecipitations were carried out on each sample. Plasticities and appearances of the sample were as follows:

Reac- Percent Plas- Sample tion Esterlfiticity, Appearance No. Time, cation mtlll minutes meters 1 10 67.3 Hard, not tacky, tacky when plasticized. 2--- 30 73. 8 Do. 3 5O 82. 4 6. 15 Do.

60 86. 7 3. 74 Hard, slightly tacky.

100 91. 0 1. 53 Very tacky. 190 95. 3 1. 25 Do. 330 97. 5 0. 98 Do.

Example IX In a polymerization vessel fitted with a reflux condenser, an electric heater, a mechanical stirrer and a thermometer were placed 29 parts of maleic anhydride and 430 parts of benzene. The mixture was heated to 70 C. Nitrogen was passed through the vessel continuously. The maleic anhydride went into solution. 26 parts of vinyl ethyl ether, which had previously been purified by multiple extraction with 5% aqueous sodium carbonate, in which ether there was dissolved 0.25 part of benzoyl peroxide, were added to the benzene solution. Polymerization commenced after 5 minutes heating as evidenced by a clouding of the solution. After 3 hours at 70 C. the reaction was substantially complete. The suspension was filtered, and the filter cake resuspended in benzene and filtered again. Yield was and intrinsic viscosity 0.5. In an esterification vessel similar to that employed in Example 1 there were placed 43 parts of the above copolymer, 61 parts n-hexyl alcohol, 3 parts p-toluene sulfonic acid, 5 parts 2,5-ditertiarybutylhydroquinone, and 172 parts xylene. The mixture was heated to boiling and refiuxed for 8 hours while collecting 5.5 parts of water. The esterification reaction was considered to be substantially complete as evidenced by low rate of water removal. The polymer ester was recovered, puritfied and dried according to the procedure in Example I. The ester was extremely tacky, almost water-white, and had plasticity of about 0.7. Percent esterification was 93%.

Example X Into the polymerization vessel of Example IX there were placed 48.5 parts maleic anhydride and 300 parts benzene. The mixture was heated to 70 C., passing nitrogen through the vessel continuously. 50 parts vinyln-butyl ether which had been washed with aqueous sodium carbonate and which contained 0.5 part benzoyl peroxide were added to the benzene solution. Polymerization commenced after 1 minute. After 3 hours of stirring at 70 C. the reaction was substantially complete. The polymer was recovered and had intrinsic viscosity of 0.68. Yield was 92% of theory. 87 parts of the copolymer ester were esterified with 168 parts n-decanol in the presence of 7.5 parts p-toluene sulfonic acid, 12.8 parts 2,5-ditertiarybutylhydroquinone, and 258 parts xylene. After 7 hours of refluxing 10.2 parts water had been collected in the azeotropic trap. The polymer ester was recovered, purified and dried. It had good tack and plasticity less than 0.65 Percent esterification was 91%.

Example XI Vinyl methyl ether-maleic anhydride copolymer, intrinsic viscosity 0.73, was esterified with n-octyl alcohol according to the procedure described in the foregoing examples. Water was removed from the azeotropic trap and degree of esterification was above 95%.

Percent Percent Plas- Cold Portion No. Peroxide G ticlty Flow,

Inches 5 94. 5 2. T5 1 78. 0 1. 63; M 7 2. 0 0. 99 M 42. 0 0. 70 7' 0 00. 0 0.

Any of the adhesives made according to any of the foregoing examples may beutilized by applying it to an adhesive-supporting. surface, plasticized where necessary, or it may be cross-linkedlto impart resistance to cold flow and applied to an adhesive supporting surface.

Although certain of the foregoing examples specify the use of an anti-oxidant during esterification, under some conditions an anti-oxidant is not required. Specifically, when the viscosity ofthe copolymer is less than one, anti-oxidant may be dispensed with without incurring undesirable degree of gelling, i. e. cross-linking during esterifications The following example illustrates preparation of polymer ester according to the invention without employing anti-oxidant.

Example XII 467 parts of vinyl methyl ether-maleic anhydride c0 polymer having intrinsic viscosity 0.73 were esterified according to the procedure described in the foregoing examples with 937 parts iso-octyl alcohol in the presence of 44 parts p-toluene sulfonic acid catalyst and 1600 parts xylene as solvent, without anti-oxidant. Refiuxing was carried on for 8 hours during which time 102 parts of water were collected in the azeotropic trap, and esterification had progressed to 97-98% completion. The esterification solution was light in color with a slightly yellowish cast. The polymer ester was recovered from solution, washed and dried. It showed no tendency to gel upon cooling and was very tacky. This adhesive was suitable for applying to an adhesive-supporting surface, or cross-linking to impart resistance to cold flow.

A remarkable feature, of the invention is the capacity of the cross-linked polymer esters to stick very tightly to what are generally considered to be stick-resistant sur- 0 faces such as glass. A particularly notable property of. the invention materials, when cross-linked, is their ability to stick very tightly even to polyethylene. On the other hand, the uncross-linked polymer esters are notable for their tendency to stick only to skin, while having minimum adhesion to such other objects and minimum ad hesion to themselves.

Another group of cross-linking agents are the diand tri-hydroxy alcohols such as the glycols (e; g. ethylene and propylene glycols and condensation products thereof such as diethylene and dipropylene glycols, etc.) and glycerol. For example, a benzene solution of the isooctyl vinyl methyl ether-maleic anhydride copolymer ester prepared according to Example II, uncross-linked, 97% csterified, plasticity 0.81 mm., is mixed with di ethylene glycol in weight amount equal to the copolymer ester (a substantial molar excess based on unesterified carhoxyl groups) and 2% p-toluene sulfonic acid based on polymer ester, in a beaker and heated with stirring to 140 C. asbenzene evaporates. Heating is continued for ,5 hour. The beaker contents are thenpoured into methanol. The cross-linked material precipitates and is reprecipitaled. several times from benzene with methanol to purify. A convenient variation is to add the polyhydric alcohol directly to the copolymer esterification reaction mixture and conti nue heating until the desired: amount of cross-linking occurs. (about 2 hours) as just described. Plasticity is 2.1 mm. Cold flow is. 0.4 inch. It will be apparent that other modifications may be made within the scope of the invention; For instance, substituted vinyl ethers, such as methyl vinyl. ethers,-when reasonably stable, polymcrizable and available, may be utilized instead of the monomers described specifically above. The invention is not limited to the illustrations presented.

The claims are:

1. An adhesive composition adapted to stick to unprimed polyvinylchloride resin film toprovide an adhesive layer surface which is characterized by tenacious adhesion to other objects including human skin but relatively little adhesion to itself, whereby upon contact of two portions of the adhesive surface they will not adhereto each other to such an extent that upon their separation from each other there is disruption of the adhesive mass and undue deformation of the film backing, said composition comprising an ester of a copolymer of. maleic anhydride and a vinyl ether having an alkyl group of 1 to 8 carbon atoms copolymerized in approximately equimolecular proportions, the copolymer having. an intrinsic viscosity in the approximate range of 0.2 to 2.0 as measured in cyclohexanone at 30 C., at least 70% of the potential carboxyl groups present in the anhydride groups in said copolymer being esterified with an aliphatic primary monohydric saturated alcohol having 6 to 16 carbon atoms said ester having, been heated in the presence of added peroxide polymerization catalyst to provide a gel content in the range of 10 to by weight, the plasticity of said composition being. not greater than about 4.0 mm. and the cold flow of said composition being not greater than 2.5 inches, said gel content being. 100 minus the percent of the adhesive composition which is removed from. 0.4 gram of the adhesive composition by mixing it with 100 cc. of benzene. allowing 'the mixture to stand without stirring for 48 hours at 30 C.,. then filtering the mixture throughLaistainless. steel wire screen of 100 mesh and separating theresidue from 25 cc. of the filtrate by evaporating this filtrate to dryness at 100 C., said plasticity being the height of a cylindrical pellet of the composition weighing 2.0 grams and having an initial diameter of 16 mm. placed on a parallel plate plastometer and maintained at. 100 F. under a load of 5000 grams measured at the end of a 14 minute period, and said cold'fiow being measured by sticking a ball of the adhesive weighing 3.0 grams 7 against a vertical glass plate and measuring the downward flow thereof at room temperature at the end of a 24 hour period.

2. A composition of clainrl wherein the alkyl'is' methyl and the alcohol isn-octanol.

3. A method of preparing the composition of claim 1 which comprises forming a solution of a copolymer of maleic. anhydride and a: vinyl ether having an alkyl group of 1 to 8 carbon atoms copolymerized in approximately equimolecular proportions in a non-aqueous solvent, the copolymer having an intrinsic viscosity in the approximate range of 0.2 of 2.0 as measured in cyclo hexanone at 30 C., incorporating in said solution an aliphatic primary monohydric saturated alcohol having 6. to 16 carbon atoms together with an esterificationcata lyst and an antioxidant, and heating the resulting, solution to esterification temperatures with removal of water of esterification from the. system until at least: 70% oi the potential. carboxyl groups present in the anhydride groups in said copolymer are esterified, recovering the resulting ester fromthe solutiomadding a peroxide poly merization catalyst thereto and heating to provide the gel content-of 10 to 100%.

4. Anadhesive product comprising an adhesive'sup' porting surface coated with an adhesive compositionadapted to stick to unprimed polyvinylchloride resin film to provide anadhesivelayer surface which is character- 13 ized by tenacious adhesion to other objects including human skin but relatively little adhesion to itself, whereby upon contact of two portions of the adhesive surface they will not adhere to each other to such an extent that upon their separation from each other there is disruption of the adhesive mass and undue deformation of the film backing, said composition comprising an ester of a copolymer of maleic anhydride and a vinyl ether having an alkyl group of 1 to 8 carbon atoms copolymerized in approximately equimolecular proportions, the copolymer having an intrinsic viscosity in the approximate range of 0.2 to 2.0 as measured in cyclohexanone at 30 C., at least 70% of the potential carboxyl groups present in the anhydride groups in said copolymer being esterified with an aliphatic primary monohydric saturated alcohol having 6 to 16 carbon atoms, said ester having been heated in the presence of added peroxide polymerization catalyst to provide a gel content in the range of 10 to 100 by weight, the plasticity of said composition being not greater than about 4.0 mm. and the cold flow of said composition being not greater than 2.5 inches, said gel content being 100 minus the percent of the adhesive composition which is removed from 0.4 gram of the adhesive composition by mixing it with 100 cc. of benzene, allowing the mixture to stand without stirring for 48 hours at C., then filtering the mixture through a stainless steel wire screen of mesh and separating the residue from. 25 cc. of the filtrate by evaporating this filtrate to dryness at 100 C, said plasticity being the height of a cylindrical pellet of the composition weighing 2.0 grams and having an initial diameter of 16 mm. placed on a parallel plate plastometer and maintained at 100 F. under a load of 5000 grams measured at the end of a 14 minute period, and said cold flow being measured by sticking a ball of the adhesive weighing 3.0 grams against a vertical glass plate and measuring the downward flow thereof at room temperature at the end of a 24 hour period.

References Cited in the file of this patent UNITED STATES PATENTS 2,454,284 Kirk Nov. 23, 1948 2,537,018 Barrett Jan. 9, 1951 2,615,843 Grammaria ..-Oct. 28, 1952 2,676,934 Butler Apr. 27, 1954 2,710,283 Linsk June 7, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,866,775 December 30, 1958 John 00 Sellers It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected belowo Column 5, line 32, for "Weight alcohol" read Weight of alcohol column '7, line 32 for cros-=linking" read cross-linking column 12, line 61, for "of 20" read to 2,0 column 13, line 18, for "100 read w 100% a Signed and sealed this 7th day of April 1959 'SEAL) ttest: KARL Ho AXLINE ROBERT C WATSON Attesting Officer Commissioner of Patents 

1. AN ADHESIVE COMPOSITION ADAPTED TO STICK TO UNPRIMED POLYVINYLCHLORIDE RESIN FILM TO PROVIDE AN ADHESIVE LAYER SURFACE WHICH IS CHARACTERIZED BY TENACIOUS ADHESION TO OTHER OBJECTS INCLUDING HUMAN SKIN BUT RELATIVELY LITTLE ADHESION TO ITSELF, WHEREBY UPON CONTACT OF TWO PORTIONS OF THE ADHESIVE SURFACE THEY WILL NOT ADHERE TO EACH OTHER TO SUCH AN EXTENT THAT UPON THEIR SEPARATION FROM EACH OTHER THERE IS DISRUPTION OF THE ADHESIVE MASS AND UNDUE DEFORMATION OF THE FILM BACKING, SAID COMPOSITION COMPRISING AN ESTER OF A COPOLYMER OF MALEIC ANHYDRIDE AND A VINYL ETHER HAVING AN ALKYL GROUP OF 1 TO 8 CARBON ATOMS COPOLYMERIZED IN APPROXIMATELY EQUIMOLECULAR PROPORTIONS, THE COPOLYMER HAVING AN INTRINSIC VISCOSITY IN THE APPROXIMATE RANGE OF 0.2 TO 2.0 AS MEASURED IN CYCLOHEXANONE AT 30*C., AT LEAST 70% OF THE POTENTIAL CARBOXYL GROUPS PRESENT IN THE ANHYDRIDE GROUPS IN SAID COPOLYMER BEING ESTERIFIED WITH AN ALIPHATIC PRIMARY MONOHYDRIC SATURATED ALCOHOL HAVING 6 TO 16 CARBON ATOMS SAID ESTER HAVING BEEN HEATED IN THE PRESENCE OF ADDED PEROXIDE POLYMERIZATION CATALYST TO PROVIDE A GEL CONTENT IN THE RANGE OF 10 TO 100% BY WEIGHT, THE PLASTICITY OF SAID COMPOSITION BEING NOT GREATER THAN ABOUT 4.0 MM. AND THE COLD FLOW OF SAID COMPOSITION BEING NOT GREATER THAN 2.5 INCHES, SAID GEL CONTENT BEING 100 MINUS THE PERCENT OF THE ADHESIVE COMPOSITION WHICH IS REMOVED FROM 0.4 GRAM OF THE ADHESIVE COMPOSITION BY MIXING IT WITH 100 CC. OF BENZENE, ALLOWING THE MIXTURE TO STAND WITHOUT STIRRING FOR 48 HOURS AT 30*C., THEN FILTERING THE MIXTURE THROUGH A STAINLESS STEEL WIRE SCREEN OF 100 MESH AND SEPARATING THE RESIDUE FROM 25 CC. OF THE FILTRATE BY EVAPORATING THIS FILTRATE TO DRYNESS AT 100*C., SAID PLASTICITY BEING THE HEIGHT OF A CYLINDRICAL PELLET OF THE COMPOSITION WEIGHTING 2.0 GRAMS AND HAVING AN INITIAL DIAMETER OF 16 MM. PLACED ON A PARALLEL PLATE PLASTOMETER AND MAINTAINED AT 100*F. UNDER A LOAD OF 5000 GRAMS MEASURED AT THE END OF A 14 MINUTE PERIOD, AND SAID COLD FLOW BEING MEASURED BY STICKING A BALL OF THE ADHESIVE WEIGHING 3.0 GRAMS AGAINST A VERTICAL GLASS PLATE AND MEASURING THE DOWNWARD FLOW THEREOF AT ROOM TEMPERATURE AT THE END OF A 24 HOUR PERIOD. 